A transfer apparatus which transfers a work between a plurality of press machines or dies arranged in series is known. As transfer apparatuses like these, there are an arm system transfer apparatus which swings an arm installed in a column etc. attached between press machines and a feed bar system transfer apparatus in which a feed bar installed in a rail etc. attached between press machines is moved horizontally or vertically. Therefore, a work is held and transferred by these arms or feed bars of the transfer apparatus. Moreover, a cross bar system transfer apparatus is known, in which a pair of transferring members (arms or feed bars) is arranged in the both sides (right and left), and a work is held by a cross bar bridged between the pair of transferring members.
In such a cross bar system transfer apparatus, since the cross bar is moved by synchronizing a pair of transferring members, a heavy strain will be put on the transferring members, the cross bars etc., and the weakest component or the most loaded component may possibly deformed or damaged, when displacement occurs between the pair of transferring members. As the cause of such displacement, the out of synchronization of the pair of the transferring members, or the contact of die etc. with a component of a press machine occurred during the movement of the transferring member can be cited.
In Patent Document 1, a transfer feeder equipped with a servo drive means which synchronizes feed bars (feed carriers) by an electrical control is disclosed, in which when an abnormality occurs in a control portion, it is switched automatically to a cam drive means which synchronizes them mechanically.
In Patent Document 2, a transfer feeder equipped with a crossbar which can easily avoid interference with the die of a press machine when transferring a work is disclosed.
In Patent Document 3, a transfer apparatus is disclosed, which comprises right and left drive devices capable of driving respectively independently, a crossbar bridged between those drive devices, a length compensation device which allows the expansion and contraction of the crossbar, and a cardan joint which connects the end portion of the crossbar and the drive device corresponding thereto. The length compensation device comprises an external tube member and an internal member. The internal member is connected to the lever of one drive device by the cardan joint. The external tube member is connected to another drive device through the cardan joint. The internal member slides inside of the external tube member in an axis direction, making the length of the crossbar extendable and contractible. The cardan joint device allows the crossbar to pivot around two axes, namely around a Y axis (transfer direction) and a Z axis (vertical direction) by each drive mechanism.